Alexandra Boltasseva

Metasurfaces have recently risen to prominence in optical research, providing unique functionalities that can be used for imaging, beam forming, holography, polarimetry, and many more, while keeping device dimensions small. Despite the fact that a vast range of basic metasurface designs has already been thoroughly studied in the literature, the number of metasurface-related papers is still growing at a rapid pace, as metasurface research is now spreading to adjacent fields, including computational imaging, augmented and virtual reality, automotive, display, biosensing, nonlinear, quantum and topological optics, optical computing, and more. At the same time, the ability of metasurfaces to perform optical functions in much more compact optical systems has triggered strong and constantly growing interest from various industries that greatly benefit from the availability of miniaturized, highly functional, and efficient …

Two-dimensional transition metal carbides, nitrides, and carbonitrides, known as MXenes, hold potential in electrocatalytic applications. Tungsten (W) based-MXenes are of particular interest as they are predicted to have low overpotentials in hydrogen evolution reaction (HER). However, incorporating W into the MXene structure has proven difficult due to the calculated instability of its hypothetical MAX precursors. In this study, we present a theory-guided synthesis of a W-containing MXene, W2TiC2Tx, derived from a non-MAX nanolaminated ternary carbide (W,Ti)4C4-y precursor by selective etching of one of the covalently bonded tungsten layers. Our results indicate the importance of W and Ti ordering and the presence of vacancy defects for the successful selective etching of the precursor. We confirm the atomistic out-of-plane ordering of W and Ti using density functional theory, Rietveld refinement, and electron microscopy methods. Additionally, the W-rich basal plane endows W2TiC2Tx MXene with a remarkable HER overpotential (~144 mV at 10 mA/cm2). This study adds a tungsten-containing MXene made from a covalently bonded non-MAX phase opening more ways to synthesize novel 2D materials.

The enhancement of second-harmonic generation from a dielectric layer embedded in a metal-dielectric-metal structure upon excitation of surface plasmon polaritons is demonstrated experimentally. The metal-dielectric-metal structure consisting of a Ge x (SiO 2) 1–x layer sandwiched by two Ag layers was prepared, and the surface plasmon polaritons were excited in an attenuated total reflection geometry. The measured attenuated total reflection spectra exhibited two reflection dips corresponding to the excitation of two different surface plasmon polariton modes. Strong second-harmonic signals were observed under the excitation of these surface plasmon polariton modes. The results demonstrate that the second-harmonic intensity of the Ge x (SiO 2) 1–x layer is highly enhanced relative to that of the single layer deposited on a substrate. Under the excitation of one of the two surface plasmon polariton modes, the …

The recent advent of tailorable photonic materials is currently driving the development of durable, compact, chip-compatible devices for information- and quantum technologies, sustainable energy, harsh-environment sensing, aerospace, chemical and oil & gas industries. In this talk, we will discuss advanced machine-learning-assisted photonic designs, materials optimization, and fabrication approaches for the development of efficient thermophotovoltaic (TPV) systems, lightsail spacecrafts, high-T sensors utilizing TMN metasurfaces and beyond. We also explore the potential of TMNs (titanium nitride, zirconium nitride) and TCOs for switchable photonics, high-harmonic-based XUV generation, refractory metasurfaces for energy conversion, high-power applications, photodynamic therapy and photocatalysis. The emphasis will be put on novel machine-learning-driven design frameworks that leverage the emerging …

A sustainable, lithography‐free process is demonstrated for generating non fading plasmonic colors with a prototype device that produces a wide range of vivid colors in red, green, and blue (RGB) ([0‐1], [0‐1], [0‐1]) color space from violet (0.7, 0.72, 1) to blue (0.31, 0.80, 1) and from green (0.84, 1, 0.58) to orange (1, 0.58, 0.46). The proposed color‐printing device architecture integrates a semi‐transparent random metal film (RMF) with a metal back mirror to create a lossy asymmetric Fabry‐Pérot resonator. This device geometry allows for advanced control of the observed color through the five‐degree multiplexing (Red‐Green‐Blue (RGB) color space, angle, and polarization sensitivity). An extended color palette is then obtained through photomodification process and localized heating of the RMF layer under various femtosecond laser illumination conditions at the wavelengths of 400 nm and 800 nm. Colorful …

Plasmonic tunnel junctions have great potential in the realization of nanoscale light-emitting devices and commonly used materials for these devices are metals such as gold and aluminum owing to their attractive optical properties in the visible range. A major drawback to their use is the unstable optical properties of their nanostructures at high current densities and elevated temperatures due to atomic motion, which hinders eventual device applications. As such, it is imperative to consider refractory alternatives that guarantee the geometric stability of the light-emitting junctions at high temperatures and mimic the optical properties of noble metals in desired wavelength regimes. Here, we present preliminary results from our study of tunnel junctions composed of refractory materials; TiN and Nb that have demonstrated desirable plasmonic responses similar to gold in the red and near-infrared regime.

The integration of solid-state single-photon sources with foundry-compatible photonic platforms is crucial for practical and scalable quantum photonic applications. This study investigates aluminum nitride (AlN) as a material with properties highly suitable for integrated on-chip photonics specifically due to AlN capacity to host defect-center related single-photon emitters. We conduct a comprehensive study of the creation and photophysical properties of single-photon emitters in AlN utilizing Zirconium (Zr) and Krypton (Kr) heavy ion implantation and thermal annealing techniques. Guided by theoretical predictions, we assess the potential of Zr ions to create optically addressable spin-defects and employ Kr ions as an alternative approach that targets lattice defects without inducing chemical doping effects. With the 532 nm excitation wavelength, we found that single-photon emitters induced by ion implantation are primarily associated with vacancy-type defects in the AlN lattice for both Zr and Kr ions. The emitter density increases with the ion fluence, and there is an optimal value for the high density of emitters with low AlN background fluorescence. Additionally, under shorter excitation wavelength of 405 nm, Zr-implanted AlN exhibits isolated point-like emitters, which can be related to Zr-based defect complexes. This study provides important insights into the formation and properties of single-photon emitters in aluminum nitride induced by heavy ion implantation, contributing to the advancement of the aluminum nitride platform for on-chip quantum photonic applications.

Intrinsic single-photon emitters in silicon nitride (SiN) have sparked considerable interest in the field of integrated quantum photonics due to their exceptional single-photon purity at room temperature and the potential for seamless integration into technologically mature SiN photonic devices. In this work, we focus on developing highly efficient single-photon sources within the SiN platform that exhibit high single-photon purity, brightness, stability, and polarization properties for applications in quantum key distribution (QKD) protocols. We applied a solid-immersion lens (SIL) approach to demonstrate ultra-bright SiN quantum emitters. We realized emitters with a saturated single-photon emission rate of on the order of MHz and, at the same time, single-photon purity quantified by second-order autocorrelation measurements yielding ag (2)(0) value of 0.07. Additionally, we explore the possibility of quantum frequency …